Lead-lag hinges or drag hinges are used on helicopter rotor blades to compensate for blade acceleration and deceleration resulting from the Coriolis effect during rotation. Lead-lag hinges include a pair of lead-lag bearings that extend over opposite ends of a lead-lag hinge pin. Each lead-lag bearing is secured in place with a separate bearing retainer, and the lead-lag bearings hold the lead-lag hinge pin in place. The lead-lag hinge extends through openings in a lead-lag link, a strap pack, and a pitch housing lug. The lead-lag hinge thereby attaches a rotor blade to a rotor assembly, while allowing the rotor blade to lead or lag the rotor assembly in rotation as the rotor blade rotates around the rotor assembly.
During use, the lead-lag hinges undergo high stresses and may be subject to fretting corrosion cracking as well as crack growth in fatigue. Failure of the lead-lag hinge pin can require emergency landing or catastrophic failure in flight. As such, the lead-lag hinges require inspection during maintenance and possible replacement to prevent catastrophic failure of the rotor assembly during use.
A lead-lag hinge with a higher strength and more robust design than previous designs would be a welcome addition to the art.